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Yield potential and stability of Australian sorghum hybrids

Australian sorghum hybrids are commonly described by seed companies based on their maturity type, tillering habit, seed colour, lodging and midge resistance characteristics. However, this information is not enough to help farmers match management practices and hybrids to sites and expected seasonal conditions. Over the last two years GRDC has invested in two QAAFI-lead projects to address this information gap; these are the Tactical Agronomy for Maize and Sorghum in the Northern Region (UQ00074), and the High Yielding Wheat and Sorghum Agronomy for the Northern Region (UQ00074) projects. The main proposition in these projects was that different combinations of cultivars (G) and managements (M), i.e. crop designs (G x M), produce different alignments between the demand and supply of water to the crop, and consequently different stress environments and final yields. The aim of these projects has been to identify the hybrid type and management combinations that maximise yield across the different growing environments in Queensland.

Ten on-farm and on-research station trials were conducted over the 2024 and 2015 seasons, where most commercial hybrids were grown under different plant populations, and row configurations (Fig 1). The data set comprises sites from the Darling Downs, Western Downs and Central Queensland. The combination of plant population, row configuration, season and site showed a yield variation between 3 and 12 t/ha, and a variation in available water between 400 and 950 mm.

Figure 1. Sorghum hybrid × environment trial at the Gatton research station in 2014-15. Contrasting environments were produced by low and high water + nitrogen inputs. Photo by J. McLean.

Differences between hybrids were largest at sites that yielded more than 8 t/ha. At lower yielding sites (3 – 8 t/ha) significant management effects (i.e. densities and configurations) were observed. At such sites treatments designed to conserve water such as single skip row configurations and planting at lower densities were generally the least effective at converting available light and soil moisture into grain. Previous research has demonstrated that these water-conserving management practices are usually most beneficial when available water restricts yields to less than 3 t/ha.

Using MR-Buster (ca. 40% market share) as a standard, we described each individual hybrid in terms of yield potential and yield stability (Fig 2). Across a wide range of MR-Buster yields (3 – 10 t/ha), the different hybrids showed more or less yield stability than MR-Buster. This is shown in Fig 3 where a trade-off is observed: stable yields can be attained but they come at the cost of reduced yield potential. Importantly, there was a close correlation between yield stability and hybrid maturity, one of the characteristics commonly reported by seed companies. Early-maturing hybrids produced lower but more stable yields than MR-Buster, whereas yields of late-maturing hybrids were highly responsive to improvements in the productivity of the environment.

Figure 2. A graphical representation of how yield stability is calculated. Yield stability is equivalent to the slope of the line describing the relationship between hybrid yield and MR-Buster yield (at the same site and subject to the same treatments) above an MR-Buster yield of 3 t/ha. Crop simulations suggest the slope of the line (β) will fall between 1.75 and 0.5. If β is greater than 1, then hybrid yield is highly responsive to changes in the productivity of the environment. If β is less than 1, then hybrid yield is relatively stable across environments. If β is equal to 1, then hybrid yield responds similarly to MR-Buster yield to changes in the productivity of the environment (black dashed line).

Figure 3: Yield stability index versus the yield of each individual hybrid, both relative to that of MR-Buster (i.e. horizontal and vertical lines through 1). For each hybrid its yield relative to that of MR-Buster was calculated for sites yielding less and more than 6 t/ha (left and right panels, respectively). Data is from multi-environment trials conducted across the Darling Downs and Central Queensland between 2014-15 and 2015-16. The yield stability index represents the hybrid response to changes in site yield as measured by the yield of MR-Buster across the range 3 – 10 t/ha. For example, hybrids with a yield stability index larger than one are more responsive than MR Buster and are better suited to highly productive sites; whereas hybrids with a value lower than one are less responsive than MR-Buster, or more stable, and expected to return more consistent yields regardless of the productivity of the site. The figure shows that there is a trade-off between yield stability and relative yield: if consistent yields are desirable they are likely to come at the cost of reduced yields overall, especially at sites yielding more than 6 t/ha.

The implication of this research is that there are likely to be different hybrids that produce greater yields than MR-Buster at the least and most productive sites across the range of environments captured in our multi-environment trial. Optimal hybrid choice thus becomes dependent on the conditions at sowing and the seasonal outlook.

The next stage of this research is to use observations from our multi-environment trial to accurately simulate the commercial hybrids that have formed the focus of our research. Attempts to reconcile modelled and observed yields and biomass suggest that at least some hybrids are surprisingly efficient at converting intercepted light into biomass. The results also suggest there is scope to improve simulated yield by refining how grain size and number are modelled.

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